It is determined that, in contrast to a frequency (for example, 800 MHz, 20000 MHz, or the like) that is used for a wireless terminal which is called a third-generation or fourth-generation wireless terminal, a millimeter-wave band, for example, such as 24.25 GHz, 28 GHz, or 39 GHz, is allocated for a frequency that is used for a next-generation (fifth-generation wireless terminal), and a technology for measuring a perception performance of the wireless terminal that uses the millimeter-wave band is required.
Generally, for the reception of the wireless terminal, a measurement is made to check whether a normal throughput can be maintained according to a change in the intensity of an incident wave, and so forth, and there is also a need to investigate whether or not an influence, which results from a change in posturing of the wireless terminal, is exerted on the incident wave, needs to be as well.
In a case where the reception performance of the wireless terminal is measured in an environment close to an actual operating environment, there is a need to specify field intensity or magnitude of an incident power (hereinafter referred to as a radio wave intensity) at a position at which a radio wave that is emitted from a measurement antenna which is positioned, away from a terminal antenna of the wireless terminal, by a distance that satisfies a distance condition of far field measurement, enters an antenna of the wireless terminal. The distance condition of far field measurement is a state where a distance R between transmission and reception antenna satisfies the following condition.R≥2D2/λwhere λ is a free space wave length (m) of a radio wave in use and D is the greater of the maximum diameters of openings of the transmission and reception antennas.
If D is set to be four times a wave length λ, R≥2D2/λ=2(16λ2)/λ=32λ. If a frequency of a radio wave is set to 30 GHz, λ=10 mm and the distance R necessary for the remote-field measurement is 32 cm or more.
However, in order to make a measurement in such a manner that entrance of an unnecessary radio wave from the outside or unnecessary reflection of the measurement signal, or the like does not exert an influence, under an environment such as a radio free-field room, processing in which radio waves with predetermined intensities or different intensities, which are emitted from the measurement antenna, are provided to the terminal antenna of the wireless terminal located at the distance R between the wireless terminal and the measurement antenna and thus a predetermined performance is obtained needs to be performed while the wireless terminal is rotated by a terminal holding rotation mechanism centering around a phase center of the terminal antenna, for example in the horizontal direction and the vertical direction, and thus the reception performance in all directions needs to be obtained.
It is noted that the phase center of the antenna is a point which is virtually considered as a concentration point of a radio wave in the emission and incidence of the radio wave, and a position thereof depends on an antenna format. For example, in the case of a dipole antenna, a vicinity of a power supply point becomes a phase center, and in the case of a horn antenna, a phase center is positioned on a slightly inner side of a horn on a central line of a horn opening portion. In an ideal antenna, the center of the antenna is determined as a single point, but in a real antenna, such points are scattered due to various reasons. Here, an average position thereof is defined as an antenna phase center, and it is considered that the position scattering of the phase center of the antenna itself is enough small to be ignored compared with other errors in a measuring system. Furthermore, in the following description, “the position of the antenna” does not represent of a physical position of the antenna having a stereoscopic or planar extension, but represents a phase center that serves as an electric function of an antenna, unless otherwise mentioned.
It is noted that the distance condition of the far field measurement is described in Non-patent Documents 1 and 2, and others.